1. Field of the Invention
Embodiments of the invention relate to a touch sensing device.
2. Discussion of the Related Art
As home appliances or portable information devices are becoming more lightweight and slimmer, user input means is being switched from a button switch to a touch screen. A touch screen includes a plurality of touch sensors.
US Publication No. 2010/0200310 (published on Aug. 12, 2010) discloses a touch screen (hereinafter, referred to as “a self capacitance touch screen”) including capacitive touch sensors at crossings of X lines and Y lines crossing each other. The self capacitance touch screen scans the X lines and converts a signal received from the X lines into digital data through an analog-to-digital conversion (hereinafter, referred to as “ADC”) process. Further, the self capacitance touch screen scans the Y lines and converts a signal received from the Y lines into digital data through the ADC process. The self capacitance touch screen recognizes a touch sensor, which is positioned at a crossing of an X line and a Y line having a large change in capacitance before and after a touch operation, as a touch position. The self capacitance touch screen analyzes digital data obtained by sensing each of an X line and a Y line and converting them through the ADC process to thereby detect the touch position. Therefore, the self capacitance touch screen may wrongly recognize a ghost point present at the same X and Y lines as an actual touch position as the touch position. Accordingly, the self capacitance touch screen has the drawbacks that it has low multi-touch sensitivity and the complicated ghost detection and a removal algorithm has to be additionally applied.
The self capacitance touch screen disclosed in US Publication No. 2010/0200310 senses the X lines and the Y lines on a group basis in a pre-scan process. Next, the self capacitance touch screen disclosed in US Publication No. 2010/0200310 performs a re-scan process and a touch position detection process after the ADC process and a touch position detection process, thereby improving the accuracy of touch recognition. Moreover, the self capacitance touch screen disclosed in US Publication No. 2010/0200310 simultaneously scans the X lines (or the Y lines) of a group in the pre-scan process, and thus may reduce a touch sensing time, as compared to a method for sequentially sensing all the X lines and Y lines each time a touch position is detected. However, the self capacitance touch screen disclosed in US Publication No. 2010/0200310 has limitation in the reduction in the touch sensing time because it has to sequentially perform the pre-scan, the ADC, the execution of the touch recognition algorithm, the re-scan, the ADC, and the execution of the touch recognition algorithm each time the touch position is detected.
A touch report rate is a frequency at which coordinate data obtained by sensing all of the touch sensors present in the touch screen is transmitted to the outside. The higher the touch report rate, the higher the continuity of touch input traces and the higher the touch sensitivity a user feels. The touch report rate is inversely proportional to total sensing time required to sense all of the touch sensors of the touch screen. That is, the longer the total sensing time, the lower the touch report rate. Accordingly, the self capacitance touch screen disclosed in US Publication No. 2010/0200310 cannot sufficiently increase the touch report rate.
The related art touch screen has the low sensing sensitivity, for example, the wrong recognition of the ghost point as the touch position and the input of a momentarily generated noise as a touch input when the momentarily generated noise is synchronized with a sensing timing. The performance improvement of the touch screen including the increase of the touch report rate, the improvement of the sensing sensitivity, etc. has to be achieved, so as to improve the touch sensitivity the user feels. For example, linearity of the related art touch screen is reduced when a line drawing or a dragging is performed on the related art touch screen.
Because the related art touch screen repeatedly senses all of the touch sensors irrespective of the presence or absence of a touch (or proximity) input, it is difficult to reduce power consumption of the related art touch screen.